The present invention generally pertains to contactless transfer of electrical energy, and more specifically, to the contactless transfer of electromagnetic energy between disparate devices by moving a magnet in one of the devices to vary a magnetic flux experienced by the other device.
Many of today""s portable consumer devices, including palm-sized computers, games, flashlights, shavers, radios, CD players, phones, power tools, small appliances, tooth brushes, etc., are powered by rechargeable batteries. The batteries in these devices, which are typically of the nickel-cadmium, lead-acid, nickel-metal-hydride, or lithium-ion type, must be recharged periodically to enable the continued use of the devices.
There are several methods used in the prior art to recharge such batteries. For example, many manufacturers produce rechargeable batteries corresponding to conventional AAA, AA, A, B, C, and D sizes, which are typically recharged using a charger station that is adapted to charge a certain size battery or a plurality of different size batteries. In addition, many power tool manufacturers produce lines of portable tools energized by batteries that are not of the standard sizes listed above, but which often share a common form factor and voltage rating. These batteries are typically recharged by removing the battery from the tool and charging it in a specially-adapted charger specific to that manufacturer""s line of tools and specifically designed to recharge batteries of that voltage. In order to recharge both conventional-size batteries and the more specialized portable power tool batteries, it is generally necessary to remove the batteries from the portable device and attach them to their respective chargers, and after they are recharged, the batteries must be reinstalled in the portable device. This task is unduly burdensome and time-consuming for the user.
In order to avoid the burden associated with the foregoing task, some portable consumer devices include a charge-conditioning circuit (either internally or externally) that can be used with a conventional power source, such as a wall outlet, to provide a conditioned direct current (DC) at a voltage suitable for recharging a battery contained in the device. For example, it is common for electric shavers to include a charge-conditioning circuit that enables a nickel-cadmium (or other type) battery retained in the shaver to be recharged by plugging the shaver into a line voltage outlet. Similarly, some flashlights have an integrated connector that allows them to be recharged by simply plugging them into a wall outlet. In addition, certain devices such as portable hand vacuum cleaners use a xe2x80x9cbasexe2x80x9d charger unit for both storing the device between uses and recharging the battery. When the portable device is stored in the base unit, exposed terminals on the device are connected through contacts on the base unit to a power supply energized with line current, thereby providing a conditioned DC current to charge the battery within the portable device.
In all of the foregoing examples, as is true of the majority of devices that use rechargeable batteries, some sort of interface comprising an electrical connection (i.e., contact) is used to provide an appropriate DC voltage for recharging the batteries. However, the use of contacts to connect a battery to a recharging current is undesirable, as they are susceptible to breakage, corrosion, and may present a potential safety problem if used improperly or inadvertently shorted. The shape and configuration of these contacts are also generally unique to individual devices, or a manufacturer""s product line, making it impractical to provide a xe2x80x9cuniversalxe2x80x9d charging interface that includes contacts.
Recognizing the problems with recharging batteries with current supplied through electrical contacts, several manufacturers now offer xe2x80x9ccontactlessxe2x80x9d battery-charging devices. These charging devices are generally of two typesxe2x80x94inductive charging systems, and infrared charging systems. Inductive charging systems include an electromagnetic or radio frequency coil that generates an electromagnetic field, which is coupled to a receiver coil within the device that includes a battery requiring recharging. For use in recharging a battery in a handheld powered toothbrush, a relatively high-frequency current is supplied to the transmitter coil in a base for the handheld toothbrush, thereby generating a varying magnetic field at a corresponding frequency. This magnetic field is inductively coupled to a receiver coil in the toothbrush housing to generate a battery charging current. Another example of such a system is the IBC-131 contactless inductive charging system by TDK Corporation, which switches a nominal 141 volt, 20 mA (max) input current to a transmitter coil at 125 kHz to produce a 5 volt DC output at 130 mA in a receiver coil.
A different contactless system for charging batteries is an infrared charging system employing a light source as a transmitter and a photocell as a receiver. Energy is transferred from the source to the receiving photocell via light rather than through a magnetic field.
Both inductive and infrared charging systems have drawbacks. Notably, each system is characterized by relatively high-energy losses, resulting in low efficiencies and the generation of excessive heat, which may pose an undesirable safety hazard. Additionally, the transmitter and receiver of an inductive charging system generally must be placed in close proximity to one another. In the above-referenced TDK system, the maximum gap between the receiver and transmitter is 4 mm. Furthermore, in an infrared system, the light source and/or photocell are typically protected by a translucent material, such as a clear plastic. Such protection is typically required if an infrared charging system is used in a portable device, and may potentially affect the aesthetics, functionality, and/or durability of the device.
It would therefore be desirable to provide a contactless energy transfer apparatus suitable for use with portable consumer devices that allows a greater spacing between the transmitter and receiver elements, and provides improved efficiency over the prior art. Furthermore, it is preferable that such an apparatus provide a contactless xe2x80x9cuniversalxe2x80x9d interface for use with a variety of different types and/or different sizes of devices made by various manufacturers.
In accord with the present invention, an energy transfer apparatus is defined that is adapted for magnetically exciting a receiver coil that includes a core of a magnetically permeable material, by causing an electrical current to flow in the receiver coil. The energy transfer apparatus includes a magnetic field generator that is enclosed in a housing and includes at least one permanent magnet. The housing is adapted to be disposed proximate another housing in which the receiver coil is disposed. A prime mover is drivingly coupled to the magnetic field generator to cause an element of the magnetic field generator to move relative to its housing. Movement of the element produces a varying magnetic field that couples with the core of the receiver coil and induces an electrical current to flow in the receiver coil.
The prime mover of the energy transfer apparatus preferably comprises an electric motor, but can include other types of devices capable of moving the element. For example, a hand crank can be employed for moving the element. In one form of the invention, the prime mover is disposed within the housing in which the magnetic field generator is enclosed. Alternatively, the prime mover is disposed remote from the magnetic field generator and is coupled to the magnetic field generator through a drive shaft.
In several embodiments of the invention, the prime mover moves the permanent magnet relative to the receiver coil. Movement of the permanent magnet varies a magnetic flux along a path that includes the receiver coil. Increasing a speed at which the permanent magnet is moved increases a magnitude of the electrical current induced in the receiver coil.
In one embodiment, the permanent magnet is reciprocated back and forth relative to the receiver coil. The reciprocating movement of the permanent magnet varies a magnetic flux along a path that includes the receiver coil.
A flux linkage bar formed of a magnetically permeable material is preferably disposed adjacent a magnetic pole of the permanent magnet. The flux linkage bar enhances the coupling of magnetic flux from a pole of the permanent magnet into a path that includes the receiver coil.
In several embodiments, the magnetic field generator preferably comprises a plurality of permanent magnets. An adjustment member is included to selectively vary a maximum magnetic flux produced by the magnetic field generator for coupling with the receiver coil. A speed control is used as the adjustment member in one embodiment.
In another embodiment, the permanent magnets include a xe2x80x9cdrivenxe2x80x9d permanent magnet that is moved by the prime mover, and a xe2x80x9cfollowerxe2x80x9d permanent magnet that is magnetically coupled to the driven permanent magnet and is moved by its motion.
In yet another embodiment, the permanent magnets are fixed relative to the housing, and the moving element comprises a flux shunt that is moved by the prime mover to intermittently pass adjacent to pole faces of the plurality of permanent magnets so as to intermittently provide a magnetic flux linkage path between the pole faces that effectively shunts the magnetic flux. When the magnetic flux is thus shunted, substantially much less magnetic flux couples to the receiver coil. The shunting of the magnetic flux through the moving element effectively periodically xe2x80x9cshuts offxe2x80x9d the magnetic field produced by the permanent magnets that would otherwise be experienced by the receiving coil, producing the varying magnetic field.
A further technique for adjusting the maximum magnetic field employs a plurality of turns of a conductor that are wound around each the plurality of permanent magnets. The plurality of turns of the conductor are connected to a source of an electrical current, producing a magnetic field that either opposes or aids the magnetic field produced by the permanent magnets, thereby varying the maximum magnetic field experienced by the receiver coil.
In yet another embodiment, the permanent magnets are radially movable relative to an axis of a drive shaft that is rotatably driven by the prime mover. The permanent magnets are attracted to each other when the shaft is at rest, but an actuator moves the permanent magnets away from each other to improve the coupling of the magnetic flux with the receiver coil when the shaft is rotating. The disposition of the permanent magnets adjacent to each other when the shaft begins to rotate reduces the startup torque required to rotate the shaft. Furthermore, by controlling the radial disposition of the permanent magnets, a magnitude of the electrical current induced in the receiver coil is selectively controlled.
According to further aspects of the invention, a contactless battery charger/energy transfer apparatus is defined that use the foregoing energy transfer scheme in combination with a conditioning circuit to recharge a rechargeable storage battery disposed in a portable device. Additionally, the energy can be supplied to electronic components in the portable device. The contactless battery charger/energy transfer apparatus typically includes a flux generator base unit, and a receiver unit. The flux generator is housed in the flux generator base unit, which in several embodiments preferably includes a xe2x80x9cuniversalxe2x80x9d mounting provision that enables the base unit to be used with receiver units of different sizes. The receiver unit comprises a receiver coil disposed in a housing adapted to mate with the base unit, and a conditioning circuit that conditions the current generated by the energy inductively coupled into the receiver coil to control the charging of a battery (or batteries) and/or provide a conditioned current to the electronic components in the portable device. The receiver coil housing may be integral to the portable device in which the receiver coil is disposed, or it may be a separate component that is suitable for attachment to a variety of different devices.
In one preferred embodiment, the flux generator base unit and receiver units are shaped in the form of tablets. The contactless battery charger/energy transfer apparatus embodiments additionally provide a sensor and an indicator for detecting and indicating when the receiver unit is mated and properly aligned with the flux generator base unit. The sensor signal controls the operation of the motor. The conditioning circuit also includes a detection circuit for determining when a battery is fully charged, and controls the charge current supplied to the battery as a function of its charge state. Also included in the flux generator base unit is a detection circuit for determining when the battery is charged, so that the motor is then turned de-energized.
According to another aspect of the invention, a wireless communication channel is effected between the receiver unit and the flux generator base unit by pulsing a load applied to the output of the conditioning circuit, thereby producing a corresponding pulse change in the current supplied to the electric motor. The pulsing current drawn by the electric motor is detected to recover the data transmitted from the receiver unit.
Another aspect of the present invention is directed to a method for charging a battery via a varying magnetic field that is inductively coupled to transfer energy to a receiver coil. The steps of this method are generally consistent with the functions provided by the elements of the apparatus discussed above.